1. Field of the Invention
The present invention relates to a discharge lamp lighting device for lighting a discharge lamp, especially, a high intensity discharge bulb (or a HID bulb) that is used as headlamps for vehicles, lighting devices for outdoor and indoor facilities, stock rooms, and factories, street lamps, and the like.
2. Description of the Related Art
A high intensity discharge bulb such as a metal halide bulb, a high pressure sodium bulb, and a mercury bulb has various features, a large luminous flux, a high lamp efficiency, and a long lifetime. They have therefore been widely used as lighting devices for outdoor and indoor facilities, stock rooms, and factories, street lamps, and the like.
In particular, recently, it has been used as a headlamp of vehicles. In order to light such a high intensity discharge bulb, it is necessary to apply a predetermined voltage to the bulb at the starting of lighting and further to apply to the bulb a high voltage pulse for the starting of lighting simultaneously. Accordingly, the discharge lamp lighting device has a ballast power source (DC/DC converter and so on) for lighting the discharge lamp with stability and an igniter (or a starter) for generating the high voltage pulse for starting.
FIG. 8 is a circuit diagram showing a conventional discharge lamp lighting device that has been disclosed in a patent document, for example, Japanese laid-open publication number 2001-284092. This discharge lamp lighting device has a power conversion section P, which includes a rectifier circuit DB, a voltage conversion circuit G, and a power conversion circuit H, a polarity reverse circuit J, a control circuit N, and an igniter G.
In order to light the HID bulb LA, first, the rectifier circuit DB rectifies a commercial power source, and converts it to a direct current voltage (or DC voltage) The voltage conversion circuit G boosts the DC voltage rectified by the rectifier circuit DB to a predetermined voltage. The power conversion circuit H converts the output voltage from the voltage conversion circuit G to a voltage of a predetermined level according to a control signal transferred from the control circuit N. The polarity reverse circuit J converts the output voltage from the power conversion circuit H to an alternative current voltage (or AC voltage). The igniter IG generates a high voltage, for example, 20 KV and adds the generated one to the output from the polarity reverse circuit J. In the conventional discharge lamp lighting device having the configuration described above, the predetermined voltage is applied into the HID bulb LA at the starting of lighting. The high voltage pulse for starting the discharge of the HID lamp LA is then added into the predetermined voltage, and the added one is applied to the HID bulb LA. In the HID bulb LA, the discharge is thereby caused in the HID bulb LA filled with gas. After this, the discharge lamp lighting device supplies a current to the HID bulb and thereby the HID bulb lights up and then enters a stable lighting.
The conventional discharge lamp lighting device described above judges the type of the HID bulb connected thereto and provides the optimum electric power to the HID bulb according to the type of the HID bulb. However, because one power source (the power conversion section P) applies the voltage to the HID bulb in both the starting of the lighting and the continuously steady lighting, it is necessary for circuit elements forming the power source (as the power conversion section P) to have both the following characteristics: a withstand voltage characteristic for withstanding the voltage at the starting of lighting; and a continuous lighting characteristic for withstanding the continuously steady lighting. This thereby increases a cost of the circuit elements forming the power source and also increases a size of the discharge lamp lighting device.
The present invention has been made to solve the above conventional drawback of the discharge lamp lighting device. It is therefore an object of the present invention to provide a discharge lamp lighting device in which one or more power sources and bridge circuit are made up of low-priced circuit elements and it is thereby possible to reduce the manufacturing cost of the discharge lamp lighting device.
In accordance with an aspect of the present invention, there is provided a discharge lamp lighting device having a power source and an igniter. The power source supplies a DC voltage or an AC voltage to a discharge lamp or bulb. The igniter applies a high voltage pulse to the discharge lamp in order to start the discharge in the discharge lamp. The power source has a starting power source and a steady lighting power source which are switched according to the condition, the starting of lighting and a continuously steady lighting. The light starting power source applies a voltage to the discharge bulb at the starting of lighting. The steady lighting power source supplies a current during the continuously steady lighting after the starting of lighting.
In accordance with another aspect of the present invention, there is provided a discharge lamp lighting device having a power source and an igniter. The power source supplies a DC voltage or an AC voltage to a discharge lamp or bulb. The discharge lamp lighting device can be applied to a discharge lamp (or a bulb) whose steady lighting voltage is not more than 60 volts. A bridge circuit in the power source is made up of withstand voltage elements of 200-250 volts. The igniter applies a high voltage pulse to the discharge lamp in order to start the discharge therein.